1. Field of the Invention
This invention relates to a method for the preparation of optically active 3-hydroxypyrrolidine derivatives (i.e., both enantiomers of optically active N-benzyl-3-hydroxypyrrolidine and also of optically active N-benzyl-3-acyloxypyrrolidine), which are useful as intermediates for the syntheses of pharmaceutical products, agricultural chemicals, and the like.
2. Description of the Prior Art
As a method for the preparation of (S)-N-benzyl-3-hydroxypyrrolidine, a synthetic process that uses L-malic acid as a raw material is known (Japanese Laid-Open Patent Publication No. 61-63652). However, in that process, a portion of the product is racemized, and therefore, optical resolution with use of D-mandelic acid must be done to improve the optical purity of the product. Another method is known that comprises the step of reducing N-benzyl-3-pyrroline with (+)-Diisopinocampheylborane, used as an asymmetric reducing agent [J. Am. Chem. Soc., 108, 2049 (1986)]. Moreover, there is a method for the derivation of (S)-3-hydroxypyrrolidine without a benzyl group at the N-position from L-glutamic acid [Synthetic Communication, 16, 1815 (1986)]. A method for obtaining (R)-3-hydroxypyrrolidine by the decarboxylation of trans-4-hydroxy-L-proline is known (Japanese Laid-Open Patent Publication No. 60-23328). Therefore, optically active N-benzyl-3-hydroxypyrrolidine can also be obtained by benzylation of these 3-hydroxypyrrolidine products. However, all of these methods require many steps and special reagents, and therefore do not permit the production of N-benzyl-3-hydroxypyrrolidine on an industrial scale.